Method of refining alloys



Patented Nov. 24, 1970 3,542,607 METHOD OF REFINING ALLOY Cedric Charles Edward Colley, Wheatley, England, assignor to Pressed Steel Fisher Limited, Cowley, xford, England, a corporation of Great Britain No Drawing. Filed Jan. 19, 1968, Ser. No. 699,057 Claims priority, application Great Britain, Jan. 25, 1967, 3,713/67 Int. Cl. C21d 1/04 US. Cl. 148-123 4 Claims ABSTRACT OF THE DISCLOSURE The structure of superplastic zinc base eutectoid or near eutectoid alloys is refined and the superplasticity is increased by subjecting the alloy to ultrasonic vibrations during the transformation period when the alloy transforms from a high temperature solid phase state to the eutectoid or partial eutectoid state after quenching from above the eutectoid temperature.

This invention relates to a method of refining the structure of those eutectoid or near eutectoid alloys that immediately after quenching from above the eutectoid temperature to ambient temperature retain the high temperature solid phase state during an incubation period prior to the start of transformation to the eutectoid or partly eutecoid state. Examples of such alloys include the eutectoid alloy or near eutectoid alloys of zinc-aluminium.

The object of this invention is to provide a method of refining the structure of such alloys in order to increase their superplasticity.

According to the invention a method of refining the structure and increasing the rate of transformation of such alloys includes the step of subjecting the alloy during the transformation period to ultrasonic vibration.

Preferably the method includes cooling the alloy during transformation by, for example, immersing the alloy in a cooling liquid to absorb the heat liberated during the transformation.

The alloy may be cooled to a temperature below ambient to extend the incubation period whereby the time before transformation commences is increased, thus givmore time before the alloy has to be subjected to ultrasonic vibration.

Embodiments of the invention will now be described solely by way of example.

EXAMPLE I A speciment cut from 0.040 inch thick zinc-aluminium alloy sheet containing 72% by weight of zinc was heated to 325 C. in a furnace for 30 minutes so that transformation in the a phase was complete. The specimen was then cooled quickly to ambient temperature in an air blast. The specimen was immediately connected to an ultrasonic vibrator working at 20,000 c.p.s. whilst transformation to the two phase part eutectoid state occurred; the air blast being maintained to keep the specimen cool during the transformation period.

Tensile tests at a strain of 1 inch/inch/minute and at 250 C. showed a maximum flow stress of 3,300 p.s.i. for the specimen compared with 3,820 psi. for a control specimen that had not been vibrated, and examination with an electron microscope showed that the structure was finer than that of the control specimen.

EXAMPLE n A specimen of zinc-aluminium alloy, containing 78% by weight of zinc was heated in a furnace maintained at 350 C. for 30 minutes so that transformation into the a phase was complete. The specimen was then quenched in cold water. After 50 seconds, just before the expiry of the incubation period, the specimen was immersed in cold water in an ultrasonic cleaning tank and was subjected to ultrasonic vibrations at 20,000 c.p.s. for 2 hours whilst transformation to the eutectoid state occurred. Examination of the specimen with an electron microscope showed that the grain structure was finer than that of a comparative specimen which had not been subjected to vibration.

Tensile tests at a rate of 1 inch/inch/minute and a temperature of 250 C. showed a flow stress of 1905 p.s.i., compared with a non vibrated control specimen which had a flow stress of 2,300 p.s.i.

EXAMPLE III A specimen of zinc-aluminium alloy containing by weight of zinc was heated in a furnace maintained at 350 C. for 30 minutes so that transformation into the a phase was complete. The specimen was then quenched in cold water and cooled to 10 C. in ethylene glycol to extend the incubation period. Twenty minutes later the specimen, still immersed in ethylene glycol at 10 C., was vibrated for 10 hours at 20,000 c.p.s. in an ultrasonic cleaning tank whilst complete transformation to the two phase part eutectoid state occurred.

Examination of the specimen with an electron microscope showed that the eutectoid structure was finer than that of a comparative specimen which had not been subjected to vibration.

What I claim is:

1. A method of refining the structure of a superplastic zinc base eutectoid or near eutectoid alloy that retains a high temperature solid phase state after quenching from above the eutectoid temperature for an incubation period preceding the start of a transformation period during which the alloy transforms to the eutectoid or partly eutectoid state, which includes the steps of:

(a) heating the alloy to a temperature above the eutectoid temperature and maintaining said temperature until transformation to a high temperature solid state is completed;

(b) quenching the alloy to a temperature below the eutectoid temperature;

(c) allowing the alloy to incubate;

(d) subjecting the alloy to ultrasonic vibrations during said transformation period.

2. A method according to claim 1, which includes the step of cooling the alloy during said transformation period.

3. A method according to claim 1 which includes the step of cooling the alloy below ambient during said incubation period.

4. A method according to claim 2 which includes the step of cooling the alloy below ambient during said incubation period.

References Cited UNITED STATES PATENTS 2,848,775 8/1958 Ettenreich ....1484

L. DEWYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner 

